What is the most accurate handgun caliber?

I was thinking about this while at the range. You see a ton of diff't calibers out here: 9mm, 40 s&w, 357 sig, 9 X18, 38 special, 44 special, 357 mag, 44 mag, 38 super. Depending on gun & shooting each one will perform pretty well, but which one is considered the most accurate, best performing and most effective as a defensive round?
I'm not looking to start a caliber war, I've just been toying w/ the idea of building a target gun and was wondering what caliber to base this project on.

Although it's not my choice for a handgun, I personally think that .357 Magnum is the most accurate pistol cartridge. That is, with all things being equal. besides, you can always practice with the cheaper .38 special. JHMO tho.

If you are just talking about putting bullets through the same hole in the target, then he most accurate calibers are rifle calibers in a bolt action pistol. Next would be your rimmed cartridges in a single shot. Then semi rimmed in a auto action. Then my favorite, straight cased rimmed cartridges in single action revolvers.

I think straight cased rimmed (44Mag) are possibly more accurate than bottle necked rimmed (44-40). Then your rimless (45ACP) would be last. Or at least it's easer make the straight cased rimmed identicle when reloading.

If you are talking about jsut hitting several targets, but fast, then it would be hard to beat a 9mm or a 45ACP. But a revolver in 38 Spec. would be close.

I think an auto action is inherently more accurate than a revolver action, but I think a rimmed revolver cartridge is more accurate than a rimmless auto cartridge if they were both shot in a single shot action.

if we bring up the Thompson/Center Contender or Encore I would submit the .429 Super Bower caliber according to Gun Tests Mr Bower used heavy .44 Bullets (thus the .429) to print unbelieveable groups at unreal ranges...but it is a wildcat

I was thinking about this while at the range. You see a ton of diff't calibers out here: 9mm, 40 s&w, 357 sig, 9 X18, 38 special, 44 special, 357 mag, 44 mag, 38 super. Depending on gun & shooting each one will perform pretty well, but which one is considered the most accurate, best performing and most effective as a defensive round?
I'm not looking to start a caliber war, I've just been toying w/ the idea of building a target gun and was wondering what caliber to base this project on.

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Its just that, there isn't any gun of all its types that are perfect for you and me but, there are guns that you can adapt to using them so that, you and the gun together, you make a; accurate, reliable, responsive and most importantly natural gun at that. Before that, you can get a PX4-Storm in 9mm if you need a gun that lack what you can adapt to, to make it perfect. Here's what this means, its that, if your gun is having a 40m range and you have to have a target kept at 320m then, go get a magnum rifle or get closer to the target. The gun's reliability is not a huge factor. Still, if you want to take on the largest military on earth in china then too, you will only need a handgun but not that, you have to shoot a round to the oil barrel near the whole army to blow them up but, do go get the grove on and use your gun to attract a small army of your own or so. See my cheeky grin as I said this poetical post and if not then, try again.

One train of thought holds that a semi-auto will be inherently more accurate (we're talking machine rest performance here) than a revolver because the chamber and barrel are exactly the same shot after shot. With a revolver, even the most precise machines will wear from cutting one cylinder to the next, giving a tiny amount of variation between consecutive shots. The only way to get a revolver to perform to it's absolute maximum consistency is to use it as a single shot, loading the same cylinder each time.

A second school of thought says the above idea is garbage.

I would look at what the winning pro's in your particular choice of competition are using, and get that type of gun. Some competition is biased toward the capabilities of semi-autos, some is not. The National Match Course, with loading five rounds at a time, is not. If all you want is pure accuracy, look at what the winners in that type of competition use for a good idea.

I'm going to guess that most of the current winners in most areas of competition are using semi-autos. That pretty much eliminates the classic rimmed revolver cartridges from consideration.

.38 S&W Special wins hands down, with .44 S&W Special following close behind (in guns chambered for the specific cartridges). Rarely will an autoloader match up with a similar quality revolver in the accuracy department; a revolvers fundamental design features lean more for accuracy. I believe this gap has started to disappear, but it is still a gap.
(I feel like I just pulled the pin out of a grenade )

A lot of your choice will depend on what form of competition you intend to participate in. Single shot bolt action handguns can do amazing things, but they probably won't win a bowling pin shoot. .22 RF handguns designed for competition, customized to the hands of the shooter, will print tiny little groups, but won't work as a self defense tool very well. A short barrel 12 gauge will excel at home defense, but won't help if you are trying for the smallest group of 10 shots off a bench. You started out asking for accuracy and worked around to defensive arms. There is no magic combination of gun and caliber that is best in every situation, only the wonderful debate of which is the best for all-around use. If you ever actually have to shoot a home invader, he/she really won't care if you can print a 2" group instead of a 4" group, so long as that group is in the critical triangle.

Maybe you need to decide which power category you are looking at. In formal match shooting, guys try to design a load to just make the minimum power rating for the category in which they intend to compete.

On the other hand, I did a fair bit of informal competition long ago. We shot the National Match course, loading 5 rounds at a time for slow, timed, and rapid fire, in centerfire and rimfire categories. One guy loved his 1911 so much he used it in the rimfire category, his logic being that he could shoot it as well as he could his .22, and the holes were larger, meaning he might pick up a couple of points since points were based on the highest scoring ring your shot cut.